Oxidative Phosphorylation: Enzymes, Complexes, and Mechanisms in Cell Respiration

Which enzyme catalyzes the formation of acetyl CoA from pyruvate?

Pyruvate dehydrogenase.

Why do red blood cells not use oxidative phosphorylation?

They lack mitochondria, so they cannot perform the CAC or oxidative phosphorylation.

Where does oxidative phosphorylation occur in the cell?

On the inner mitochondrial membrane and in the matrix.

What are the two main parts of oxidative phosphorylation?

1) Electron Transport Chain (ETC) and 2) ATP synthesis via ATP synthase.

What is the purpose of the electron transport chain?

To create a proton gradient (proton motive force) by pumping H⁺ into the intermembrane space.

How many integral membrane protein complexes are in the ETC?

Four (Complexes I-IV) plus two electron carriers (ubiquinone and cytochrome c).

Which complex contains succinate dehydrogenase from the CAC?

Complex II.

What is coenzyme Q (ubiquinone)?

A non-protein electron carrier that exists as oxidized Q or reduced QH₂ and ferries electrons from Complex I and II to Complex III.

Why does FADH₂ generate fewer protons than NADH in the ETC?

FADH₂ enters at Complex II, bypassing Complex I, so fewer protons are pumped (6 vs. 10).

What is the final electron acceptor in oxidative phosphorylation?

Molecular oxygen (O₂), which is reduced to water.

How many protons are pumped per NADH and per FADH₂?

NADH: ~10 H⁺; FADH₂: ~6 H⁺.

What is the proton motive force?

The electrochemical gradient of protons across the inner mitochondrial membrane that stores free energy for ATP synthesis.

What are the two domains of ATP synthase and their roles?

F₀: Rotating proton channel in the membrane; F₁: Stationary catalytic domain that synthesizes ATP.

How many protons are needed to make one ATP?

Approximately 4 H⁺.

How many ATP molecules are produced per NADH?

About 2.5 ATP.

What percentage of ATP from glucose oxidation comes from oxidative phosphorylation?

About 87% (26 out of 30 ATP).

What happens when the proton motive force is disrupted?

ATP synthesis decreases, heat may be generated (e.g., in brown adipose tissue), and free radicals can form.

Name two ways oxidative phosphorylation can be inhibited.

Poisons that block electron flow (Complexes I, III, IV) and uncouplers like DNP that short-circuit the proton gradient.